OCR Text |
Show Scanning electron micrographs taken at intermediate stages of combustion confirmed the postulated reaction sequence, suggesting that adhesion occurs as an oxide / sulfide melt, with oxidation ultimately to hematite occurring within the deposit. The laboratory experiments also provide direct evidence for particle fragmentation during combustion and the production of particles in the submicron range. However, additional experimentation will be required to elucidate the role of vaporization/recondensation in the formatin of submicron fume. Several issues need to be further clarified, including the role of associated carbon on pyrite transformation. Also, it will be important to theoretically investigate the effect of fragmentation as noted in the laboratory experiments. It is anticipated that both the resulting fragment size distribution and the potential presence of carbon will influence pyrite oxidation rates. Irrespective of whether or not carbon is present, pyrite decomposition rates to pyrrhotite would be similar. The oxidation of pyyrhotite, however, would be delayed until the carbon is consumed and the sulfide portion is exposed. The temperature of the transforming pyrite inclusion during this process will be determined by the coal particle temperature, which would be high enough to melt the pyrrhotite. One would expect therefore that the delayed oxidation would prolong the presence of a melt state when carbon is associated with pyrite. ACKNOYLEDGMENTS This work was supported by the u.s. Department of Energy, Pittsburgh Energy Technology Center, on Contract No. DE-AC22-86PC907S1. 12 |